For a number of years airbags have been installed in a number of automotive vehicles as a safety feature and their use is increasing greatly. As a matter of fact, the Surface Transportation Safety Act requires passenger and driver side airbags on all passenger cars by the 1998 model year and on light trucks by the 1999 model year.
While in the past such airbags have employed a pyrotechnic-type inflator, more recently inflators of a hybrid-type have been employed. A hybrid-type inflator houses both a highly pressurized inert gas, such as argon and helium, stored in a pressure vessel and also a pyrotechnic gas-generating material. In operation, in one embodiment, when a sensor detects an imminent collision and thus the need for immediate inflation of the airbag, the pyrotechnic material is ignited forming a heated gas which ruptures a seal and is directed into the stored pressurized gas in the pressure vessel, which stored gas is heated and expanded from ambient temperature by the igniter gas. The heated, expanded gas in the pressure vessel reaches a pressure sufficient to rupture a second seal thereby permitting flow of the gas into a folded airbag for inflation and deployment thereof. An advantage of the hybrid-type inflator system is its lower cost and the fact that it generates less heat in the airbag than a pyrotechnic-type inflator.
The use of hybrid-type inflators for airbag modules has produced a number of challenges. Among these challenges is the ability to pressurize and seal a highly-pressurized pressure vessel at an appropriate level of pressurization and to do so in such a manner as to avoid weld leaks. Prior to the present invention, one method of filling and sealing of such a pressure vessel for a hybrid-type inflator of an airbag module employed a system and apparatus for supplying a single welding ball at a time through a seal system to the opening to be welded while maintaining an insulated seal around the opening of the pressure vessel to prevent leakage of the high pressure gas and to guard against shorting and arcing. In general, in such a system, a ball is dropped into a conical-shaped gas passage port or opening in the inflator pressure vessel and subject to resistance welding by moving a retracted welding electronic element of the apparatus into an extended welding position and thereafter supplying a welding current to said welding electrode to weld the ball in the gas passage port or opening and thereby seal same and thereafter retracting the welding electrode and restoring the ball delivery system. Such a welding system is disclosed, for example, in U.S. Pat. No. 5,196,669, issued Mar. 23, 1993 to Ronald W. Richardson and assigned to RWC, Inc. of Bay City, Mich., and is currently marketed by said company as its Model 6000 Pressurized Fill Welding Machine.
However, it will be appreciated that the aforedescribed process and apparatus is complex. Numerous drawbacks exist with such a process and apparatus in addition to their complexity. For example, the welding balls are occasionally not properly aligned in the pressure vessel port or opening, the welding process produces a product with a definite fusion line and cracks are often formed or developed along the fusion boundary or fusion line. Moreover, such apparatus is complex and expensive to produce and does not always readily permit the manufacture of pressurized vessels in an easy, effective and efficient manner.
It would therefore be desirable to provide an improved method and apparatus for filling a pressure vessel to a relatively high pressure level and weld sealing the gas passage or opening in the pressure vessel without the need for additional filler material. It would also be desirable to provide such an improved method and apparatus whereby weld cracks are avoided or substantially eliminated. It would be even more desirable to provide such an improved method and apparatus which requires no moving parts and thus is easy to produce and operate. A still more desirable object would be to provide an improved method and apparatus for filling an airbag module inflator pressure vessel with an inert gas to a pressure of 2850 psi or greater and weld sealing the inert gas passage or opening in the inflator pressure vessel and to do so without additional filler material so as to avoid or substantially eliminate cracks in the weld by employing an apparatus requiring no moving parts.
In the process of this invention for supplying and filling a metal pressure vessel with an inert gas to a high level of gas pressurization through a gas passage or opening in the wall surface of the pressure vessel and then weld sealing said gas passage or opening, a groove feature is provided on the wall surface of the pressure vessel, which groove surrounds and is slightly spaced apart from the gas passage or opening such that the metal of the wall surface of the pressure vessel between or intermediate the groove and the gas passage or opening provides filler material for filling and sealing the gas passage or opening when subjected to appropriate welding conditions, such as, for example, tungsten-inert gas or laser or electron beam welding conditions.
Another aspect of this invention is a novel fill head/welding apparatus for accomplishing such process of supplying and filling a pressure vessel with an inert gas through a gas passage or opening in the wall surface of the pressure vessel to a high level of gas pressurization and then weld sealing said gas passage or opening, wherein said fill head/welding apparatus requires no moving parts. The fill head/welding apparatus surrounds and sealingly engages a portion of the outer metal wall surface of the pressure vessel containing the gas passage or opening and the groove surrounding the gas passage or opening. The apparatus comprises a housing providing a chamber, said housing having a gas inlet, a gas outlet and an electrode port. A suitable welding element is fixedly mounted in the apparatus housing and extends into the electrode port in the housing to a location essentially adjacent the gas passage or opening in the pressure vessel wall on which the fill head/welding apparatus is sealingly engaged.
Although the method and apparatus of this invention are especially useful for filling and sealing a highly-pressurized pressure vessel, it will be understood that the method and apparatus can find usefulness in other conditions. That is, the method of employing a groove feature on the wall surface of a vessel surrounding a gas passage or opening may be used to more effectively weld shut openings in low or non-pressurized vessels or even in vacuum vessels.